DESCRIPTION: Like many serious yet uncommon diseases, we remain largely ignorant of causal risk factors for SLE. Unfortunately, robust studies of rare disease often face insurmountable obstacles, especially recruitment of sufficient numbers of incident cases, and identification of appropriate controls. New ways of circumventing these barriers could facilitate studies of disorders like SLE and stimulate progress in these fields. The rapid expansion in Internet-use, and technological refinement, have made this interactive modality a powerful resource for performing questionnaire-based research among geographically dispersed participants. As such, one particularly alluring application of the Internet is the conduct of case-control studies online. A methodologic consideration which favors this approach is that valid case-control studies can be performed in special subsets of the population. On the other hand, the validity of this approach is predicated on the ability to recruit control samples that are representative of the source population, and participants in a way that is independent of the exposures of interest. Our goal is to evaluate these methodologic factors by performing a model internet-based case-control study of SLE and knee OA. A. Since the internet-based approach has greatest appeal in the study of rare disorders, we will test the feasibility of recruiting sufficient numbers of individuals with SLE, and will describe the characteristics of these participants, including associations with a panel of SLE-related epiphenomena. B. However, since risk factors for SLE are not well established, we will use the osteoarthritis evaluation to test the construct validity of this approach by seeing whether it can detect documented risk factors for this common disorder. Please note that the exposure assessments are being used in this study to evaluate the feasibility and construct validity of this approach, and not to test etiologic hypotheses. C. Finally, we will evaluate the validity of our recruitment approach by testing to see whether all cases and controls are derived from the same source population.